Use of electrical storage devices such as secondary batteries contributes to effective use of energy. In recent years, for example, photovoltaic power generation systems have been actively developed as environmentally-friendly clean energy. However, photoelectric conversion modules for converting solar light into electric power, which usually have no electrical storage function, are sometimes used in combination with secondary batteries. Effective utilization of energy is made, for example, by charge and discharge control for charging the secondary batteries with electric power generated by the photoelectric conversion modules while discharging the electric power from the secondary batteries in response to a request from an external load or the like.
When the electrical storage systems are thus constructed in combination with the secondary batteries and power sources to perform the charge and discharge control, it is desirable to monitor or diagnose any abnormality in the systems.
For example, Patent Document 1 discloses, as an electrical storage system using a secondary battery such as a lithium ion secondary battery, a structure including a self-diagnostic means that checks the presence or absence of an abnormality inside the electrical storage system, a means that measures a voltage across terminals of the secondary battery, an electrical current passing through the battery, and a temperature related to the battery, a charge and discharge controlling means connected to a positive side charging line, a system controlling means, an inverter connected to the charge and discharge controlling means, and a communication means for devices that performs bidirectional communication with the devices to which electric power is supplied from the inverter. Here, it is described that after self-diagnosis, whether or not the voltage across terminals, the electric current, and the temperature show any abnormality is checked. When no abnormality is found and discharging is allowed, whether or not to perform discharge is checked. Then, when discharging is determined, discharge processing is performed, or when discharging is not determined, it is checked whether or not to perform charge. When charging is determined, charge processing is performed.
Patent Document 2 describes a microcomputer for receiving a signal from a current sensing circuit to detect an amount of charge in an electrical storage system using 100 to 150 lithium ion secondary batteries, and a process of turning on a main switching element while turning off a start-up switching transistor when a voltage of each lithium ion secondary battery exceeds an overdischarge setting value. Further, it is also described that a bypass circuit is provided to prevent an overrun of a withstanding voltage from being caused by turning off the main switching element when the voltage of each lithium ion secondary battery exceeds the overdischarge setting value.